1. Field of the Invention
The present invention relates to a short range pulse radar device and a component thereof, which can improve accuracy of short range measurement.
2. Background Art
A pulse radar device generates a transmission pulse wave, transmits the transmission pulse wave from an antenna toward an object to be detected, and receives by the antenna a pulse wave (reflected wave) reflected by the object to be detected during a detection time period. The received reflected wave is detected by a heterodyne method, a homodyne method, or the like. The detected reflected wave is amplified by a baseband amplifier unit. After that, the amplified reflected wave is converted into a digital signal by an analog-to-digital (A/D) converter circuit. The converted digital signal is input to a CPU and is used for detecting a distance, a relative speed, or the like by software.
The baseband amplifier unit of the pulse radar device is required to amplify the reflected wave with a relatively large gain so as to obtain a sufficient level for the A/D conversion, thereby securing accuracy in measurement of distance. In this case, the transmission pulse wave sneaking into the amplifier circuit or switching noise caused by switching between transmission and reception in the pulse radar device is applied to the baseband amplifier unit as an interference signal. As a countermeasure against this phenomenon, the amplifier is desired to amplify the signal only during the detection time period. However, because of charge and discharge within the amplifier circuit or its peripheral circuit, it is difficult to control the gain of the amplifier at high speed. Therefore, a technology to remove the interference signal is demanded.
As a method of removing the interference signal, there is a technology disclosed in Japanese Patent Laid-Open No. 2007-139691, for example. In this technology, conduction and cut-off of the received signal is controlled by a switching element in synchronization with the transmission pulse wave, and thereafter a falling edge of a pulse waveform of the received signal is delayed. Then, reception control means performs the A/D conversion of the received signal with a delay of a predetermined period of time after starting conduction of the reception signal.